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Abstract:

The present invention comprises methods and compositions for making a
silver-containing antimicrobial hydrophilic material. More particularly,
the present invention comprises methods and compositions for stabilized
silver antimicrobial devices comprising a matrix comprising a polymer
network and a non-gellable polysaccharide, and an active agent. The
matrix may be formed into any desired shape for its desired uses.

Claims:

1-20. (canceled)

21. A biocompatible antimicrobial matrix, comprising a hydrophilic
cross-linked polymer network and a metal colloid incorporated in the
matrix, wherein the metal colloid is formed by the direct reaction of an
anion and a metal cation, and wherein the anion is in an excess
concentration of the metal cation, such that association of the metal
cation and the anion is favored.

22. The matrix of claim 21, further comprising an active agent.

23. The matrix of claim 21, wherein the hydrophilic cross-linked polymer
is polyacrylamide.

36. The matrix of claim 21, further comprising a water loss control agent,
a plasticizer, or a hydration control agent.

37. A wound care device comprising an antimicrobial cross-linked
hydrophilic polymer network, and a metal colloid directly incorporated in
the matrix, wherein the metal colloid is formed by the reaction of an
anion and a metal cation, and wherein the anion is in an excess
concentration of the metal cation, such that association of the metal
cation and the anion is favored.

38. The device of claim 37, wherein the polymer is polyacrylamide.

39. A biocompatible antimicrobial matrix, comprising a hydrophilic
cross-linked polyacrylamide polymer network, a non-gellable
polysaccharide, and a silver chloride colloid incorporated in the matrix,
wherein the silver chloride colloid is formed by the direct reaction of a
chloride anion and a silver cation, and wherein the chloride anion is in
an excess concentration of the silver cation, such that association of
the silver cation and the chloride anion is favored.

40. The matrix of claim 39, further comprising an electron acceptor.

41. The matrix of claim 39, further comprising a water loss control agent,
a plasticizer, or a hydration control agent.

42. The matrix of claim 39, further comprising an active agent.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is a continuation of U.S. application Ser. No.
10/978,556, filed Nov. 1, 2004, now allowed, which is a continuation of
U.S. patent application Ser. No. 10/441,275, filed May 19, 2003, now U.S.
Pat. No. 6,897,349, which is a continuation of U.S. patent application
Ser. No. 09/675,892, filed Sep. 29, 2000, now U.S. Pat. No. 6,605,751,
which claims the priority of U.S. Provisional Patent Application No.
60/212,455, filed Jun. 19, 2000, and U.S. Provisional Patent Application
No. 60/157,000 filed Oct. 1, 1999, and which is a continuation-in-part of
U.S. patent application Ser. No. 09/191,223 filed Nov. 13, 1998, now U.S.
Pat. No. 6,355,858, which is a continuation-in-part of U.S. patent
application Ser. No. 08/971,074, filed Nov. 14, 1997, now U.S. Pat. No.
5,928,174, which are herein incorporated by reference in their entirety.

FIELD OF THE INVENTION

[0002]The present invention relates generally to antimicrobial devices and
methods for making and using such devices and particularly to
compositions and methods for delivering active agents to wounds. More
particularly, the present invention relates to methods of making
antimicrobial matrices for uses in many areas, including treatment of
wounds.

BACKGROUND OF THE INVENTION

[0003]The outer layer of skin surrounding the body performs an important
protective function as a barrier against infection, and serves as a means
of regulating the exchange of heat, fluid and gas between the body and
external environment. When skin is removed or damaged by being abraded,
burned or lacerated, this protective function is diminished. Areas of
damages skin are conventionally protected by the application of a wound
dressing which facilitates wound healing by acting as a skin substitute.

[0004]Wounds to skin and the underlying tissues of humans and animals may
be caused by external insult such as friction, abrasion, laceration,
burning or chemical irritation. Damage to such tissues may also result
from internal metabolic or physical dysfunction, including but not
limited to bone protrudence, diabetes, circulatory insufficiencies, or
inflammatory processes. Normally tissue damage initiates physiological
processes of regeneration and repair. In broad terms, this process is
referred to as the wound healing process.

[0005]The wound healing process usually progresses through distinct stages
leading to the eventual closure, and restoration of the natural function
of the tissues. Injury to the skin initiates an immediate vascular
response characterized by a transient period of vasoconstriction,
followed by a more prolonged period of vasodilation. Blood components
infiltrate the wound site, endothelial cells are released, exposing
fibrillar collagen, and platelets attach to exposed sites. As platelets
become activated, components are released which initiate events of the
intrinsic coagulation pathway. At the same time, a complex series of
events trigger the inflammatory pathways generating soluble mediators to
direct subsequent stages of the healing process.

[0006]Normally, the wound healing process is uneventful and may occur
regardless of any intervention, even in the case of acute or traumatic
wounds. However, where an underlying metabolic condition or perpetual
insult such as pressure or infection are contributing factors, the
natural wound healing process may be retarded or completely arrested,
resulting in a chronic wound. Trends in modern medical practices have
shown that the wound healing of both acute and chronic wounds may be
significantly improved by clinical intervention using methods and
materials that optimize wound conditions to support the physiological
processes of the progressive stages of wound healing. Key factors in
providing the optimal conditions are the prevention of scab formation,
prevention or control of microbial activity, and the maintenance of an
optimal level of moisture in the wound bed. It is also helpful to manage
wound exudate fluid.

[0007]A common problem in the management of both acute and chronic wounds
is the maintenance of an optional level of moisture over the wound bed
during heavy exudate drainage. This is usually, but not always, an early
stage of healing. Most moist wound dressing technologies such as thin
films, hydrocolloid dressings and hydrogels are typically overwhelmed by
the accumulated exudates moisture during this heavy drainage phase.
Management of moisture during heavy exudate drainage often necessitates
the use of gauze or sponge packings that wick away excess moisture from
the wound bed, thin film coverings that trap exudate fluid over the wound
bed, or calcium alginate dressings that chemically bind exudate moisture
due to the hydroscopic properties of the seaweed extract.

[0008]Examples of wound dressings that have been developed include
collagen dressings, a natural polymer. Soluble collagen has been used as
a subcutaneous implant for repairing dermatological defects such as acne
scars, glabellar furrows, excision scars and other soft tissue defects.
Collagen has also been used in many forms as wound dressings such as
collagen sponges. Several inventions have attempted to solve the problem
of maintenance of an optimal level of moisture-in the-wound environment.
Collagen is used as the matrix material in Artandi, U.S. Pat. No.
3,157,524 and Berg et al., U.S. Pat. No. 4,320,201. However, most of
these dressings are not satisfactory for the various types of full
thickness wounds. Collagen films and sponges do not readily conform to
varied wound shapes. Furthermore, some collagen wound dressings have poor
fluid absorption properties and undesirably enhance the pooling of wound
fluids. Generally, most wound dressing materials do not provide for the
control or elimination of microbial bioburden in the wounds.

[0009]Another example of wound dressings that have been developed for
control of moisture levels in wounds are the hydrocolloid dressings.
United Kingdom Patent Number 1,471,013 and Catania et al., U.S. Pat. No.
3,969,498 describe hydrocolloid dressings that are plasma soluble, form
an artificial eschar with the moist elements at the wound site, and
gradually dissolve to release medicaments. These dressings comprise a
hydrophilic foam of dextran polymer that can be applied without
therapeutic agents or ointments, are non-irritating to the lesion and can
be easily removed.

[0010]Known hydrocolloid dressings in general, and the Catania et al.
dressings in particular, are subject to a number of drawbacks. The major
disadvantages of these dressings include the potential to disintegrate in
the presence of excess fluid at the wound site, and minimal, virtually
negligible, control over water loss from the wound. This latter
disadvantage is particularly important, as excess water loss from a wound
will cause an increase in heat loss from the body as a whole, potentially
leading to hypermetabolism. In addition, hydrocolloid dressings require
frequent dressing changes. This is especially true of the Catania et al.
dressing due to the dissolution of the dextran polymer at the wound site
caused by the fluid loss through the wound in the exudative stage.

[0011]Although currently available dressing materials possess features
that contribute to the control of heavy exudate drainage, most also
possess significant limitations that retard the overall healing process.
For example, thin film dressings such as those described in U.S. Pat. No.
3,645,835, maintain excessive moisture over the wound bed, contributing
to the overhydration or maceration of surrounding skin. Although sponges
and gauze support tissue, they require frequent changing, and cause
irritation to the wound bed during body movement and dressing removal.
These dressings may be permeable to moisture but not to microorganisms.
Although these devices and others administer some control over wound
exudate moisture and may additionally provide a barrier to microbial
contamination, they do not actively participate in controlling the growth
of microorganisms or in the elimination of microbial bioburden from the
wound dressing. Calcium alginates turn into a gelatinous mass during
interaction with moisture, are difficult to remove completely, and often
dehydrate the wound bed due to the hydroscopic nature of the matrix.

[0012]Importantly, none of the presently available devices significantly
contribute to or support the autolytic debridement phase, which is the
natural removal process of necrotic tissue and debris from the wound.
Autolytic debridement is a key early stage event that precedes repair
phases of healing. When wound conditions are not optimal for supporting
autolytic debridement, then clinical procedures such as surgical removal,
irrigation, scrubbing, and enzymatic or chemical methods must be used to
remove the necrotic tissue and escar that can inhibit wound healing.

[0013]Temporary or permanent wound dressings that are designed to enhance
wound healing are needed to cover large open wounds on patients with
extensive bums, lacerations and skin damage. Furthermore the ability to
produce wound dressings in a variety of shapes to accommodate multiple
sizes and forms of injuries is important in the manufacture of useful
medical products.

[0014]In addition, there continues to be a need for a wound dressing that
possesses high moisture absorption capacity, a high rate of absorption,
as well as a capacity to regulate moisture at the wound bed-dressing
interface. Desirably, such a wound dressing device should stimulate the
autolytic debridement process, especially during the heavy exudating
phase of wound care management.

[0015]Another desirable aspect of a wound dressing would be the ability to
deliver active agents to the site of injury to accelerate wound healing
and in particular to control the growth and damage caused by microbial
contaminants of the wound. Active agents for use in wound treatment may
be administered to an individual in a variety of ways. For example,
active agents may be administered topically, subingually, orally, or by
injection (subcutaneous, intramuscular or intravenous). Nevertheless,
there are drawbacks to many of these methods, and an inexpensive,
reliable, localized and relatively pain-free method of administering an
active agent has not been provided in the prior art.

[0016]One common method employed for the treatment of wounds is the
topical application of a salve or ointment. Yet many times, topical
application to a wound can be painful and short-lived. Additionally, in
the case of a deeply cavitated wound in particular, an excess of active
agent may be required because the agent must diffuse through layers of
necrotic tissue and newly forming epidermal tissues. This difficulty in
delivering the agent may require the application of an excessive amount
of the agent and preclude an accurate determination of the effective
amount of active agent to be added.

[0017]The oral and sublingual administrations of active agents used in
wound treatment also have their drawbacks. Most importantly, the
administration site, the mouth, is normally far removed from the actual
location of the wound. Ingestion of an active agent at a site distant
from the wound may result in the agent having negative system-wide
effects and possibly knocking out the normal flora, or normal microbial
environment, whose presence benefits an individual. Successful absorption
of the agent into the bloodstream also depends on several factors such as
the agent's stability in gastrointestinal fluids, the pH of the
gastrointestinal tract, solubility of solid agents, intestinal motility,
and gastric emptying.

[0018]Injection of an active agent, a normally painful method of
administration, may have the same negative system-wide effects as that of
an oral or sublingual administration if injection is at a site distant
from the wound. Yet more importantly, a danger inherent in the injection
of an active agent is that rapid removal of the agent is impossible once
it is administered. There is also a risk of transmission of infections
and the possibility of vascular injury due to the use of needles.

[0019]One active agent, silver, has long been recognized for its broad
spectrum anti-microbial activity and compatibility with mammalian
tissues. Although silver has been used in a large range of medical
devices, its incorporation, as a prophylactic anti-infective agent, in
primary wound contact products has been restricted due to silver's
adverse properties. These properties include a short half-life, the rapid
inactivation of silver by protein, and light-mediated discoloration of
the product containing silver and any body parts touching the product,
such as skin. Recently, manufacturers have tried methods to overcome some
of the limitations to broaden the utility of silver in wound care. The
currently available silver-containing wound care dressing materials have
been unsuccessful in adequately overcoming the problems inherent in using
silver.

[0020]Medical devices that are implanted or those that are attached to
epithelial may create an environment conducive to the multiplication and
growth of microorganisms. This microbial growth may lead to complications
such as local or systemic infection. Dermal wounds are at particular risk
since microbial contaminants are commonly present, and the wound produces
optimal nutrients and other environmental conditions for microbial
growth. Medical practices have demanded the use of sterile or low
bioburden devices and the adoption of procedures and adjuncts such as
frequent dressing changes, use of topical antimicrobial compounds, and
systemic antibiotics to control growth of microorganisms on and around
the device during use.

[0021]An alternative approach is the production of devices that possess
broad spectrum antimicrobial activity. A variety of approaches have been
taken to endow devices with antimicrobial properties including soaking of
indwelling catheters and other devices in antibiotics such as penicillin
or fluconazole, or in antiseptic solutions such as chlorhexidine or
sulfadiazine. Although these approaches render some antimicrobial
activity to the devices, they are of limited utility due to toxicity,
stability and effectiveness. Such limitations include short half-lives in
tissue or on the devices, the agents' spectrums of activity are too
narrow for the range of organisms that may be encountered near the
device, or the agents may be destructive to tissues at their effective
concentrations.

[0022]Heavy metals may provide an optimal alternative as antimicrobial
agents for rendering medical devices with antimicrobial properties. Heavy
metals may exist as salts, complexes with carriers, as base metals or
other forms. This versatility contributes to the variety of ways in which
the forms can be coupled with the devices. In addition, it is known that
heavy metals such as gold, platinum, silver, zinc and copper exert
antimicrobial activity at very low concentrations against a broad
spectrum of organisms including bacteria, protozoa, fungi and viruses (N.
Grier, "Silver and its compounds" In Disinfection, Sterilization, and
Preservation, (3rd edition S. S. Block, ed., Lea & Febiger,
Philadelphia, Ch. 20, (1983).). Silver is oligodynamic, meaning that it
has antimicrobial activity at very low concentrations against a wide
range of bacteria, fungi and viruses. Measurements of ionic silver as low
as 10-6 to 10-9 M have been shown to be antimicrobial (A. D.
Russel and W. B. Hugo, "Antimicrobial Activity and Action of Silver",
Prog. in Med. Chem. 31:351-370, 1994.) Moreover silver is well tolerated
by mammalian cells and tissues.

[0023]One active heavy metal, in particular silver, has long been
recognized for its broad spectrum anti-microbial activity and
compatibility with mammalian tissues. Although silver has been used in a
large range of medical devices, its incorporation, as a prophylactic
anti-infective agent, in primary wound contact products has been
restricted due to silver's adverse properties. These properties include a
short half-life, the rapid inactivation of silver by protein, and
light-mediated discoloration of the product containing silver and any
body parts touching the product, such as skin. Recently, manufacturers
have tried methods to overcome some of the limitations to broaden the
utility of silver in wound care. The currently available
silver-containing wound care dressing materials have been unsuccessful in
adequately overcoming the problems inherent in using silver.

[0024]The mode of action of silver is due to the reactivity of the ionic
form with a variety of electron donating functional groups that contain
reactive entities such as oxygen, sulfur or nitrogen. Electron donating
functional groups in biological systems are many and varied, including
groups such as phosphates, hydroxyl, carboxylates, thiol, imidizoles,
amines, and indoles. Microbial macromolecules are richly endowed with
these functional groups that, when bound by silver ion, may become
inactivated and dysfunctional resulting in the death of the
microorganism. Ionic silver is known to disrupt microbial cell wall, cell
membrane, electron transport, metabolic and anabolic enzymes, and nucleic
acid function (A. D. Russel, W. B. Hugo, "Antimicrobial activity and
action of silver" In Progress in Medicinal Chemistry. Vol. 3, G. P. Ellis
& D. K. Luscombe, ed., Elsevier-Science B. V., (1994)).

[0025]Oligodynamic silver has been incorporated into medical inventions
for the purpose of imparting an antimicrobial effect. The use of metallic
silver was reported in UK patent application No. 2134791A which describes
the vapor deposition of metallic silver or silver/carbon on Sphagnum moss
for the purpose of making an antimicrobial surgical dressing. U.S. Pat.
No. 5,753,251 describes the production of a wound contact product by
sputter coating silver on to substrates such as plastic films to impart
antimicrobial activity to the device. A description of a metallized
bandaging material, prepared by vapor coating metallic silver onto a
fiber fleece was described in U.S. Pat. No. 2,934,066. U.S. Pat. No.
4,483,688 describes the combining of finely ground metallic silver with a
binding agent for coating indwelling catheters.

[0026]Alternative means of incorporating silver or silver salts into or on
devices have also been described. The incorporation of antimicrobial
silver into the adhesive of an adhesive coated, moisture impermeable thin
film polymer for use for securing medical devices or as a wound dressing
was described in U.S. Pat. No. 4,340,043. The use of silver oxide, finely
ground into small particles, dispersed in latex batching has been
described in U.S. Pat. No. 4,902,503 for use in making indwelling medical
devices where antimicrobial activity would increase effectiveness.

[0027]Although these devices have provided certain solutions to combining
antimicrobial activity with medical devices, these inventions have
identified a number of limitations associated with silver and silver
salts. The highly reactive nature of silver ions contributes to the
relatively short half-life of the antimicrobial effect in the presence of
certain functional groups. Moreover its antimicrobial form, ionic silver,
is unstable in light and is rapidly converted to a black inactive
precipitate by photo-reduction.

[0028]Attempts at overcoming the limitations of silver addition included
applying silver or silver salts onto dry substrates where little or no
ionization of silver could occur or the use of substrates containing few
reactive functional groups that would react with ionic silver. However,
this is impractical for applications where moisture abounds such as in
moist devices such as soft contact lenses, hydrated plastic implants, or
in moist wound dressing cover such as a hydrogels; hydrocolloids, or
biologics, or in medical devices that contain reactive functional groups
such as in a collagen matrix.

[0029]To overcome these problems, inventions describing stabilization of
silver have been described. U.S. Pat. No. 5,863,548 describes the process
of forming a complex between silver and allantoin which in turn is
encapsulated in allantoin to form a light stable antimicrobial coating
for medical devices. U.S. Pat. No. 5,709,870 describes a process for
producing a light and heat stable silver complex with
carboxymethylcellulose for use in coating fibers. Similarly U.S. Pat. No.
5,744,151 describes a process for rendering silver photo-stable and
antimicrobial for use as an adjunct to pharmaceuticals by forming an
acyclic polyether polymer stabilized by ratios of cation and anions in
the process.

[0030]The stabilization of the antimicrobial effect of silver in a device
that is exposed to light or is in contact with functionally reactive
groups may also be accomplished by retarding the release of the silver
ion into the environment around the device after application. In other
words by using mechanisms that continuously release a small steady supply
of ionic silver into the device. An invention described in U.S. Pat. No.
5,470,585 incorporates silver into a form of glass that slowly dissolves
in the presence of moisture. The slow dissolution of the matrix thereby
releases ionic silver about the device. Sputter coated nanocrystalline
silver coatings on devices such as plastics for wound care initially are
similarly slowly released from the device during contact with moisture of
tissues to liberate ionic silver around the device during use as is
described in U.S. Pat. No. 5,753,251.

[0031]These inventions have provided some solutions to the problems of
stability, and half-life for silver for several silver antimicrobial
applications. However they are cumbersome, may contain toxic accessory
agents that support function, or are prohibitively expensive for
application to commodity medical devices such as wound dressings.
Moreover, these approaches are not solutions to the incorporation of
antimicrobial silver into devices that contain solvents where ionization
of the silver would normally occur in wound dressings such as hydrogels,
moist contact lenses, oral prosthetics and other devices containing
water. In addition, these inventions make only marginal contribution to
the sustained continuous release of ionic silver from devices treated by
the processes described. What is needed are compositions and methods for
providing antimicrobial activity in medical devices, and particularly for
silver incorporation into medical devices such as moisture-containing
wound dressings, skin contact devices, such as monitor leads, wound
dressings and hydrated plastic implants.

SUMMARY OF THE INVENTION

[0032]The present invention comprises compositions and methods for
producing materials that contain stabilized antimicrobial metals,
preferably silver, for many uses, including medical products. In
particular, the present invention provides methods and compositions for
administering active agents, such as antimicrobial silver, to the site of
a wound via wound dressings. The present invention also allows for
localized delivery of active agents and prevents the negative effects of
system-wide administration. The present invention comprises wound healing
devices that have specialized structures that aid in treatment of wounds.

[0033]A preferred embodiment of the present invention comprises a
hydratable matrix material that has an antimicrobial agent, such as a
heavy metal, most preferably, silver, incorporated into the matrix. The
matrix preferably also comprises components that stabilize and control
the release of the active agent into the surrounding environment when
used.

[0034]In a preferred embodiment of the present invention, active agents
are incorporated directly, or may be incorporated by sequentially adding
components or precursors of the active agent to the matrix of the
devices, and having the precursors form the active form of the active
agent in or on the matrix. The agents may be incorporated by absorption
or adsorption of agents or precursors by the matrix, and preferably by
incorporation during the polymerization of the matrix. It is theorized
that the release of the active agents may be controlled via manipulation
of concentration parameters, movement of water through the matrix and the
degree of cross-linking in the matrix. In another preferred embodiment,
the wound dressings comprise a stranded configuration, wherein the
strands extend from at least one common region and the strands themselves
comprise a polymer matrix.

[0035]The wound dressing devices of the present invention may be used to
simultaneously deliver a number of active agents to a wound site. Wound
healing agents such as antimicrobial agents, antifungal agents, antiviral
agents, growth factors, angiogenic factors, anaesthetics,
mucopolysaccharides and other wound healing proteins may be incorporated
into the wound dressings for controlled release. Adjuvants and other
agents, such as those that boost the immune system, may also be
incorporated into the wound dressings devices of the present invention. A
surprising and novel aspect of a preferred embodiment having agents
directly incorporated into micro-cavities of the matrix is that the
activities of the wound healing agents are not altered by incorporation
into the devices and that the agents are effective upon their release.

[0036]In a preferred embodiment of the present invention, the wound
dressing devices of the present invention comprise a novel stranded
structure made from a matrix suitable for application to broken skin and
underlying tissues. The individual strands of the preferred embodiment
may or may not have free floating ends, however, the unique arrangement
of the device allows it to both absorb excess wound exudate, and
simultaneously conform closely to the walls of the wound bed, in order to
accelerate overall wound healing.

[0037]A stranded configuration of the wound dressings of the present
invention is particularly desirable because the novel design provides a
high surface area to volume ratio to maximize interchange between the
matrix and wound moisture and wound debris. The multiple strands of the
preferred configuration provide maximal inter-strand space to serve as a
reservoir for moisture, necrotic materials, or agents scheduled for
delivery to the wound bed. The superior moisture absorption and
regulation capacity of the preferred embodiment equip the wound dressing
devices for use on heavily to moderately draining wounds.

[0038]In addition to increased moisture absorption and the ability to
deliver active agents, the individual strands of the preferred
configuration may participate in mechanical debridement thereby
accelerating the wound healing process. The individual strands of the
preferred wound dressings increase the inherent flexibility of the
device, and enhance conformability to the irregularities of the contours
in the wound cavity, allowing the preferred devices to be used in deeply
cavitated wounds where debridement is essential. In order to simplify the
overall wound dressing procedure, the preferred devices may have a single
unit construction that is applied and removed as a complete unit, leaving
no remnants. Additionally, the preferred devices may be left in place for
prolonged periods between changes.

[0039]Other forms of the matrices of the present invention, such as molded
articles, are also contemplated by the present invention. Other forms
also include films, sheets, fibers and amorphous gels. The matrices of
the present invention can be dipped or applied in methods known to those
skilled in the art to articles or devices.

[0040]A preferred embodiment of the present invention comprises methods
and devices that incorporate antimicrobial agents, more preferably, the
agents are heavy metals, and most preferably, the agents are silver
compositions. The silver-containing devices have antimicrobial activity,
are resistant to light degradation, possess sustained release
characteristics, and provide improved wound healing ability. Methods of
the present invention comprise methods for making the antimicrobial
devices, such as wound dressings, and methods of use of such devices.

[0041]Another preferred embodiment of the present invention comprises
devices and methods for making and using such devices that comprise
materials that allow for the application and stabilization of
antimicrobial metals such as silver. Preferred embodiments comprise
devices made with or associated with hydrophilic pre-formed fibrous
materials. A preferred use is for use in medical and non-medical devices
and materials for the purpose of imparting sustained, light stable
antimicrobial activity to the device. In particular, the present
invention relates to compositions and methods for the incorporation and
stabilization of silver onto and within the hydrophilic fibers of
cross-linked and non-cross-linked celluloses such as carboxymethy
cellulose and hydroxymethyl cellulose, cotton, rayon, and of fibers made
from polyacrylates and other synthetic and natural polymers, and fibers
of calcium alginates that may be used as a primary contact
sustained-release silver antimicrobial materials.

[0042]Additionally, the methods incorporating stabilized heavy metals,
particularly silver, into materials can be used for a wide variety of
products. For examples, such methods include adding antimicrobial
characteristics to cosmetic products, such as dressings, topical lotions,
or compresses for acne and blemishes, scar reduction, tattoo removal, and
laser resurfacing, any body- or skin contacting medical devices, such as,
catheter coatings, guidewire coatings, ostomy appliances, respiratory and
feeding appliances, contact lenses, and hearing aids; and personal and
skin care products, such as skin conditioners, barrier creams,
lubricating preparations, and super absorbents for addition to diapers,
adult incontinence products, and feminine hygiene products.

[0043]Accordingly, it is an object of the present invention to provide
compositions and methods for the treatment of wounds.

[0044]Another object of the present invention is to provide compositions
and methods that facilitate and accelerate the wound healing process.

[0045]Yet another object of the present invention is to provide a wound
dressing device wherein active agents are incorporated.

[0046]It is another object of the present invention to provide wound
dressing devices that absorb excess moisture at a wound site.

[0047]It is another object of the present invention to provide wound
dressing devices that promote autolytic debridement.

[0048]Yet another object of the present invention is to provide a wound
dressing device that absorbs wound exudate by allowing for optimal
contact between the device and the wound area.

[0049]A further object of the present invention is to provide wound
dressing devices for external and internal wounds.

[0050]Another object of the present invention is to prevent infection by
providing wound dressing devices that clean wound sites by removing
debris and contaminating material.

[0051]It is another object of the present invention to provide wound
dressing devices that easily conform to the shape of a wound.

[0052]It is yet another object of the present invention to provide wound
dressing devices that are easily manufactured.

[0053]Still another object of the present invention is to provide wound
dressing devices that may be easily removed from wounds and replaced.

[0054]Yet another object of the present invention is to provide wound
dressing devices that are compatible with injured tissue and do not
induce irritation or inflammation.

[0055]It is yet another object of the present invention to provide wound
dressing devices that function to both absorb wound exudate and promote
autolytic debridement.

[0056]Another object of the present invention is to provide methods and
compositions for making single unit construction wound dressing devices
having multiple strands.

[0057]It is another object of the present invention to provide methods and
compositions for treating wounds using wound dressing devices that
function to both absorb wound exudate and deliver wound healing agents.

[0058]An object of the present invention to provide methods and
compositions for treating wounds using wound dressing devices having
active agents incorporated therein.

[0059]Still another object of the present invention is to provide methods
and compositions for delivering active agents to wound sites and damaged
tissue.

[0060]An object of the present invention comprises methods and
compositions for providing devices with antimicrobial activity.

[0062]Still a further object of the present invention comprises methods
and compositions for providing devices that are essentially dry with
antimicrobial activity.

[0063]These and other objects, features and advantages of the present
invention will become apparent after a review of the following detailed
description of the disclosed embodiments and the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

[0064]FIG. 1 is a three dimensional view of one embodiment of a wound
dressing device of the present invention wherein the multi-stranded
device may have free floating strand ends.

[0065]FIG. 2 presents a cross-section of a strand of the multi-strand
device.

[0066]FIG. 3 is an illustration of a pattern of a die used for cutting a
device from an appropriate matrix material.

[0070]FIG. 10 shows graphs of the absorbency and moisture-donating ability
of a preferred embodiment of the present invention.

[0071]FIG. 11 shows the effect of a silver-containing device on the
viability of an E. coli culture.

[0072]FIG. 12 is a graph showing the effect on the bioburden when using a
silver-containing device.

DETAILED DESCRIPTION

[0073]The present invention comprises compositions and methods for making
and using materials comprising antimicrobial activity. Such materials may
be hydrophillic moist materials or dry materials. In particular, the
present invention comprises compositions and methods for making and using
such materials, for example for treating wounds using wound dressing
devices with active agents incorporated therein. A preferred active agent
is silver that is incorporated into the materials and is stabilized until
released by application or placement in the site of use. In a preferred
embodiment, the active agents may be directly incorporated into the
scaffolding matrix of the devices for controlled release at the site of
the wound. In a further preferred embodiment, the matrix comprises a
biocompatible, scaffolding polymer network, such as a polyacrylate
hydrophilic polymer, with a non-gellable polysaccharide dispersed evenly
throughout said network. Most preferably, the matrix has antimicrobial
activity associated with it. The matrices of this preferred embodiment
provide a reliable and efficient means for delivering active agents to
the site while at the same time may also provide a superior moisture
regulation capacity which is important for promoting wound healing.

[0074]The wound dressing devices of the present invention are preferably
in the form of a continuous sheet form, similar to wound dressings known
in the art. However the invention may also take other particular
conformations. For example, a preferred embodiment of the present
invention comprises a stranded configuration wherein the individual
strands extend from at least one common region and may have free-floating
ends. This particular conformation is particularly suitable for use in
deeply cavitated wounds since the multiple matrix strands enable the
dressing to conform to individual and uniquely shaped wound areas.
Furthermore, the devices accelerate wound healing by displacing and
allowing for the removal of excess cellular exudate and debris,
thereby-improving-the rate of tissue repair and regeneration.

[0075]The terms "a", "an" and "the" as used herein are defined to mean one
or more and include the plural unless the context is inappropriate.

[0076]Active Agents

[0077]The active agents incorporated into the matrices and devices of the
present invention may be used for a variety of applications where there
is a need for the presence of the active agent. A particularly preferred
use is in the treatment of wounds or in skin healing. The active, agents
may participate in, and improve, the wound healing process, and may
include antimicrobial agents, including but not limited to antifungal
agents, antibacterial agents, anti-viral agents and antiparasitic agents,
growth factors, angiogenic factors, anaesthetics, mucopolysaccharides,
metals and other wound healing agents.

[0081]Proteins that may be especially useful in the treatment of wounds
include, but are not limited to, collagen, cross-linked collagen,
fibronectin, lanminin, elastin, and cross-linked elastin or combinations
and fragments thereof. Adjuvants, or compositions that boost an immune
response, may also be used in conjunction with the wound dressing devices
of the present invention. Antibodies or antibody fragments are also
included.

[0082]It is to be understood that in a preferred embodiment of the present
invention, the active agent, more preferably heavy meatls, most
preferably silver, is incorporated into the matrices or devices so that
the agent is released directly from the devices and delivered to the
contact substrate such as the wound site or application site. The
incorporated agents may be released over a period of time, and in this
way, the devices retain their ability to kill or inhibit microorganisms
over an extended period of time. As used herein, the term silver includes
all silver salts or silver compounds, including, but not limited to,
silver chloride, silver phosphate, silver sulfate, silver iodide or
silver bromide. The active form of the silver salt is the silver ion, as
is the case for the active forms of the heavy metals.

[0083]Administering active agent for the prevention or control of local
infection using the wound dressing itself overcomes several of the
problems of the prior art. First, the present invention avoids the
painful re-application of salves and ointments to the wound. The present
invention also allows silver to be delivered directly into the site of
the wound to prevent the negative impact of system wide delivery of the
agents as encountered after oral or intravenous administration. In the
case of deeply cavitated wounds, in contrast to the topical application
of active agents, the wound dressing and silver therein may be located
directly within the wound, providing a more effective delivery of the
agents. Finally, in contrast to an injection of active agents, the
present invention provides methods of administering active wherein the
agents may be removed immediately from the wound and the administration
terminated.

[0084]Matrices

[0085]The devices of the present invention comprise a hydrophilic matrix
material, preferably, one that is flexible and elastic, and is of a
semi-solid scaffold that is permeable to substances such as inorganic
salts, aqueous fluids and dissolved gaseous agents including oxygen. The
substances permeate the matrix through movement via intermolecular spaces
among the cross-linked polymer. The matrix may be moist or dry.

[0086]Preferably, the hydrophilic matrix material is constructed from a
natural or synthetic polymer and a non-gellable polysaccharide. Natural
hydrophulic polymers that may be used for the construction of the wound
device include, but are not limited to collagen, animal hide, hyaluronic
acid, dextran and alginate. Additionally included are hydrophilic fibers
of cross-linked and non-cross-linked celluloses such as carboxymethy
cellulose and hydroxymethyl cellulose; cotton, rayon, and of fibers made
from polyacrylates; and fibers of calcium alginates that may be used as a
primary contact sustained release silver antimicrobial material.
Synthetic polymers that may be used include, but are not limited to
polyacrylarmide, polyvinyl's (PVP, and PVC), polyacrylate, polybuterate,
polyurethane foam, silicone elastomer, rubber, nylon, vinyl or cross
linked dextran. If cross-linked dextran is used, it is preferred that the
molecular weight of the dextran polymer is between 50,000 and 500,000.
The most preferable non-gellable polysaccharide is a non-gellable
galactomannan macromolecule such a guar gum. A range of guar gum between
approximately 0.01 kg to 100 kg, preferably between approximately 0.1 kg
to 10 kg, and most preferably between approximately 0.5 kg to 2 kg is
generally sufficient. Other non-gellable polysaccharides may include
lucerne, fenugreek, honey locust bean gum, white clover bean gum and
carob locust bean gum.

[0087]To decrease the permeability of wound dressing devices comprising a
cross-linked polymer and non-gellable polysaccharide matrix, water loss
control agents may be applied to the surface of the device. Application
of water loss control agents is preferred since a decrease in the
permeability of the device controls the loss of fluids from the wound.
The preferred water loss control agent is petrolatum, however, other
water loss control agents such as glycolipids, ceramides, free fatty
acids, cholesterol, triglycerides, sterylesters, cholesteryl sulfate,
linoleic ethyl ester and silicone oil may also be used.

[0088]If desired, a plasticizer may also be added to the matrix material.
A preferred plasticizer is glycerol and water, however, propylene glycol
and butanol may also be used. If glycerol is used, a range of between
approximately 0.5 kg to 50 kg, preferably between 1 kg and 30 kg, and
most preferably between approximately 5 kg to 15 kg is generally
sufficient. The plasticizer may be added in the initial mixture of
polymer and cross-linking agent.

[0089]If desired, a hydration control agent may be incorporated into the
matrix. The preferred hydration control agent is an isopropyl alcohol,
however, ethanol, glycerol, butanol, and propylene glycol may also be
used. A range of isopropyl alcohol of between approximately 0.1 kg to 10
kg, preferably between approximately 0.2 kg to 5 kg and most preferably
between approximately 0.5 kg to 2 kg is generally sufficient.

[0090]The matrix of the preferred embodiment preferably comprises
polymerized chains of acrylamide monomer, wherein the acrylamide monomers
are cross-linked with a cross-linking agent, a non-gellable
polysaccharide, and an active agent or pharmaceutical directly
encapsulated into micro-cavities therein. A range of acrylamide between
approximately 1 kg to 100 kg, preferably between approximately 2 to 50
kg, and most preferably between approximately 5 kg to 20 kg is generally
sufficient. A preferred matrix comprises a cross-linked polyacrylamide
scaffolding that enmeshes guar gum as disclosed in U.S. Pat. No.
5,196,160 to Nangia.

[0091]The most preferable cross-linking agent is NNNN'
methylenebisacrylamide, however other appropriate cross-linking agents
such as bisacrylylycystaimine and diallyltartar diamide may also be used.
If NNNN-methylenebisacrylamide is used, a range of between approximately
0.01 kg to 1 kg, preferably between approximately 0.02 kg to 0.5 kg, and
most preferably between approximately 0.05 kg to 0.3 kg is generally
sufficient. As noted above, the most preferable non-gellable
polysaccharide is a non-gellable galactomannan macromolecule such a guar
gum, but other non-gellable polysaccharides may include lucerne,
fenugreek, honey locust bean gum, white clover bean gum and carob locust
bean gum.

[0092]Ammonium persulfate and TEMED may also be added to the matrix. A
range of ammonium persulfate between approximately 0.01 kg to 1 kg,
preferably between approximately 0.02 kg to 0.5 kg, and most preferably
between approximately 0.05 kg to 0.2 kg is generally sufficient.
Additionally, a range of TEMED between approximately 0.01 kg to 1 kg,
preferably between approximately 0.02 kg and 0.5 kg, and most preferably
between approximately 0.05 kg to 0.3 kg is generally sufficient.

[0093]Incorporation of Active Agents

[0094]One embodiment of the matrices of the present invention can be found
in U.S. Pat. No. 5,196,190 to Nangia et al., which is hereby incorporated
in its entirety. Nangia et al. teach a matrix composed of a natural or
synthetic polymer, a non-gellable polysaccharide, and a
phospholipid-based drug delivery system. In particular, Nangia et al.
teach a matrix capable of drug delivery, wherein lipid vesicle liposomes
containing a desired drug are incorporated into the matrix.

[0095]One problem with the prior art methods, however, is the difficulty
of incorporating active agents into the liposomes since some agents may
be incompatible with liposome chemistry. Incorporation using liposomes is
time consuming, expensive and sometimes unreliable because dispersion of
the liposomes in the matrix is difficult to achieve and once achieved,
the liposomes may prematurely release costly agents due the liposomes'
inherent instability. Another problem is that the prior art fails to
teach a method of incorporating active agents into a wound dressing
wherein the release of the agent over time can be controlled through the
manipulation of concentration parameters, movement of water through the
matrix and the degree of cross linking in the matrix.

[0096]Preferred embodiments of the present invention however, address the
need for a less expensive, quicker, and more reliable method for
incorporating a wider range of desired agents into matrices and devices.
Preferred embodiments also provide a means to control the release of the
desired agents over time via manipulation of concentration parameters,
movement of water through the matrix and the degree of cross-linking in
the matrix. In a preferred embodiment, the desired agents may be directly
incorporated into the matrix by adding the agents into the initial
formulation for the matrix prior to cross-linking. This method of
incorporation is inexpensive, rapid and reliable, and most surprisingly,
the incorporated agents are not affected by the process of polymerization
and retain their biological activities. Another preferred method of
incorporation is the adsorption or absorption of solutions containing the
active agents or precursors of the active agent to an already formed
matrix.

[0097]Using preferred embodiments of the present invention, delivery of
the desired agents may be controlled by the use of movement of liquid
through the matrix. Though not wishing to be bound by any theory, it is
theorized that the liquid in a matrix of polymer and non-gellable
polysaccharide is either bound to the non-gellable polysaccharide or it
is unbound in the polymer mass. Thus, it is theorized that the present
invention uses the free liquid portion of the matrix as a general solvent
and as a means to deliver desired agents. Soluble drugs are easily
dissolved in the free liquid portion, however slightly soluble drugs are
ground to a fine powder and may require the use of a wetting agent such
as glycerol or isopropyl alcohol or a surfactant such as polysorbate,
triton-X or sodium lauryl sulfate.

[0098]Once the desired active agent or agents are dispersed throughout the
matrix, a portion of the agent resides in the non-gellable
polysaccharide, while another portion of the agent is dissolved in the
free liquid phase and moves freely through the matrix. The ability of the
agent to move freely throughout the matrix in the free liquid phase is
important in the agent delivery system of the present invention. Because
the agent is dissolved in the free liquid phase, a concentration gradient
of the active agent is created between the matrix of a wound dressing
device and the moisture of the wound itself. Therefore, when the matrix
is placed onto a moist surface such as an open wound, the soluble agent
will move through the free liquid phase toward the agent-free wound
moisture, resulting in the delivery of the agent to the wound. This
movement of soluble agent further upsets the equilibrium between soluble
and insoluble agents, and causes more agent to dissolve into the free
liquid phase, thus causing more agent to be delivered to the wound.
Because the present invention incorporates the desired agent directly
into the matrix rather than incorporating the drug into other delivery
vehicles, such as liposomes, the agent may be dissolved in the free
liquid phase and reliably delivered to the wound through the process
described above.

[0099]Delivery of the desired agents may also be controlled by the degree
of cross-linking in the matrix. As described above, the desired agents
may be added to the other ingredients forming the matrix prior to the
addition of the cross-linking agent. Subsequent addition of the cross
linking agent and concomitant polymerization results in both chain
elongation of monomeric chemicals and cross-linking between chains of
monomers. The combination of chains cross-linked together creates
micro-cavities wherein the desired agents are encapsulated. By
controlling the amount of cross-linking agent and the length of chains of
monomer, it is possible to regulate the size of the micro-cavities in the
polymer. Larger micro-cavities, produced by a lower degree of
cross-linking, allow for freer migration and quicker delivery of the
desired agent, whereas smaller micro-cavities increase the delivery time.
Although the liposome based delivery system may also make use of the
degree of cross-linking, the liposome itself acts as an additional
barrier to delivery, making delivery less controlled and less reliable.

[0100]The present invention comprises compositions that are useful for
stabilization of heavy metals, particularly silver, for devices that have
sustained release characteristics, are light stable, and possess
antimicrobial activity. In particular, this invention relates to the
incorporation and stabilization of silver salts into a hydrated
polyacrylate matrix that may be used as a primary contact sustained
release silver antimicrobial material for use in wound dressings and
other devices and materials.

[0101]The polyacrylate matrix as taught in the Nangia patent, U.S. Pat.
No. 5,196,190, has little or no antimicrobial properties when applied to
wounds. A preferred embodiment of the present invention comprises the
incorporation of antimicrobial silver into the matrix to increase its
effectiveness and utility for application such as in wound care where
microbial growth may inhibit or complicate the wound healing process. The
preferred polyacrylate matrix, like many hydrated medical devices,
contains a significant amount of aqueous moisture. This moisture serves
as a solvent in which many of the undesirable characteristics of silver
are exhibited. These include the formation of ionic silver which is
highly reactive to functional groups that exist on organic material that
may be part of the device; the formation of the photo-reactive form (Ag+)
of silver that may lead to discolorization; a solvent phase that
contributes to the instability of silver to certain levels of heat; as
well as the transfer of antimicrobial silver to adjoining packaging
materials through migration of silver through the solvent phase.
Preferred methods and devices of the present invention comprise addition
of compositions comprising metals, preferably silver, that are added to
hydratable medical devices such as hydrogels to provide stable sustained
release antimicrobial activity.

[0102]The present invention contemplates devices comprising metals, and a
preferred metal is silver. Though silver is taught as a preferred
embodiment, the present invention comprises use of any metal that imparts
antimicrobial activity to a matrix or device. It has been found that
silver salts such as silver chloride are generally stable in the salt
form. Moreover, many silver salts such as silver phosphate and silver
sulfate are only weakly soluble in aqueous solvent. Methods of the
present invention comprise preparing a salt of silver during the
preparation of the matrix, and preferably the matrix is a hydratable
polyacrylate polymer.

[0103]The formation of the weakly soluble salt, silver chloride, is fully
dispersed throughout the matrix and provide the precursor for the
formation of the sustained release silver. The deposition of collodial
silver chloride or other weakly soluble salt throughout the matrix is
accomplished by any one of several methods of the present invention. In
one method, the pre-formed salt, such as silver chloride, may be
incorporated along with other components during the compounding of the
matrix formulation prior to polymerization. Another method comprises
sequentially adsorbing or absorbing solutions comprising the precursor
components, such as weakly soluble salts into a matrix. For example, a
solution containing chloride ions is added to a polymerized hydrophilic
matrix, where the solution is adsorbed or absorbed by the matrix. A
second solution, containing silver ions, is added to the matrix to form a
colloid of silver chloride in the matrix. Another method, and a preferred
method, is the sequential addition of anions and cations during the
compounding of the material mixture, causing the formation and dispersion
of the colloid in the mixture prior to polymerization.

[0105]An ionic silver solution comprises compositions such as those
prepared by dissolving a salt of silver, including but not limited to
silver nitrate, silver acetate, silver citrate, and silver sulphate, into
water. The silver ions may also be added in a dry form.

[0106]When the polymer is catalyzed to gel, the finely dispersed silver
chloride is immobilized within the polymer where it undergoes
disassociation (as an example according to the formula):

→AgCI→Ag+Cl.sup.

[0107]Since AgCl is only weakly soluble in aqueous solutions the
re-association to AgCI is strongly favored. However the ionic form is
unstable and may react to light to form insoluble elemental silver
(Ag°). This form has minimal antimicrobial activity and moreover
is a black precipitate that strongly discolors the matrix when it is
formed. In addition the ionic form (Ag+) is highly reactive with
functional electron donating groups which may reduce its antimicrobial
effect. Therefore it is desirable to stabilize the silver in hydrated
polymers such as the preferred embodiment, by providing an excess of
chloride ions in the matrix to favor association rather than
disassociation.

[0108]Although excess chloride ions in the matrix provide conditions that
favor the formation of the stable silver chloride salt form of silver, an
amount of free ionic silver exists in the matrix. The ionic form (Ag+)
may react with electron donors leading to a steady conversion of ionic
silver into non-antimicrobial forms and left to continue would
significantly deplete the matrix of a source of antimicrobial silver. The
reaction of ionic silver with strong electron donating groups such as
light, can be inhibited by the incorporation of a competing electron
acceptor that has a higher electrochemical potential than silver in the
matrix. In the preferred embodiment, either ionic copper or ionic iron
are both strong electron acceptors that may be incorporated into the
matrix to stabilize ionic silver in the matrix until it is applied to a
moist environment such as a wound. The electron acceptors are added to
the matrix solution in a stabilizing solution. A stabilizing solution is
a solution that provides components, including but not limited to the
electron acceptors, that aid in the prevention of the reaction of the
active agent. For example, in a preferred embodiment, a stabilizing
solution comprises a solution of electron acceptors such as a copper
chloride or ferric chloride solution, for addition to a silver-containing
matrix mixture to aid in the prevention of the reaction of ionic silver.
Alternatively, a stabilizing solution also comprises the addition of
electron acceptors, such as copper chloride or ferric chloride, in a dry
form, not in a liquid solution. Additionally, a stabilizing solution
comprises one or more electron acceptors for prevention of reaction of
the active agent.

[0109]Other electron acceptors that can be used in the present invention
include, but are not limited to, gold, platinum and cesium. Other strong
organic oxidizers may be used to prevent the reduction of ions, such as
the reduction of silver by light energy.

[0110]A preferred embodiment of the present invention comprises a wound
healing device comprising a polyacrylate hydratable matrix produced
according to U.S. Pat. No. 5,196,190 with antimicrobial properties
provided by incorporating heavy metals, preferably silver. Other
preferred embodiments comprises devices that are coated with matrices,
preferably a biocompatible polymeric matrix comprising a scaffolding
polymer network with antimicrobial activity. A non-gellable
polysaccharide may or may not be included with the matrix.

[0111]A silver containing polyacrylate matrix generally comprises mixing
approximately 100-250 g acrylamide and approximately 0.5 to 5.0 g
bisacrylamide into 2800 to 3950 g of water containing between 6 to 54 g
of sodium chloride. To this mixture, add 21 g of guar and 188 g of
glycerol.

[0112]After mixing to homogeneity, slowly add an aqueous solution
containing approximately 0.01-3.1 g silver nitrate to the mixing batch.
Alternatively, molar equivalents of silver acetate, silver citrate or
silver sulfate may be substituted for silver nitrate. After formation of
the finely dispersed silver complex, dissolve either from about 0.1 to
2.8 g copper chloride (CuCl2) or about 0.3 to 3.3 g ferric chloride
FeCl3. Alternatively, molar equivalents of potassium chloride,
magnesium chloride, zinc chloride, calcium chloride, hydrochloric acid or
other soluble chloride salt may substituted for the ferric or copper
chloride. The polymerization of the mixture into a polymer is
accomplished by blending approximately 0.7 to 3.6 ml TEMED and about 0.2
to 4.6 g ammonium persulphate into the mixture. The mixture is poured
into the appropriate molds with the desired shape before polymerization
in a dark place. The gelled polymer is typically removed from the mold,
dehydrated by mild heat in a darkened drier and then rehydrated by
humidification to a desired moisture content, approximately 15 to 50%
w/w. The matrix may cut into a desired size or shape, packaged and then
is sterilized by irradiation with an electron beam or gamma irradiation.

[0113]The present invention also comprises compositions and devices
comprising preformed hydrophillic fibers and methods for making and using
such materials with antimicrobial activity. Pre-formed cross-linked
hydrophilic fibers have been shown to have utility in wound care due to
their absorbency of wound fluid and their compatibility with exposed
tissues. Many hydrophilic fibrous materials are readily available through
commercial channels for on-processing, packaging and sterilization for
use in wound and other medical applications. However none of these
materials are available with silver impregnation due to the instability
of silver and due to the lack of effective known methods for the
incorporation of stabilized silver into the substrates of these materials
prior to fiber formation. Furthermore these materials have little or no
inherent antimicrobial activity. Therefore the most practical method for
rendering these materials antimicrobial would be the application of
silver in a stabilized form to the pre-formed fibers. U.S. Provisional
Patent Application No. 60/157,000, herein incorporated in its entirety,
describes a method of incorporation of antimicrobial silver
into-materials, preferably polyacrylate materials, by the formation of a
silver chloride colloidal precipitate during the compounding of the
matrix material. The silver complex was stabilized by a combination of
excess copper and chloride ions. The incorporation of a stabilized form
of silver colloid into pre-formed hydrophilic fibrous materials is
impractical. Therefore this invention also comprises methods for the
incorporation of silver into fibrous materials by an impregnation method
that causes the in situ formation of a stabilized silver colloid complex
within and around the fibrous material.

[0114]One method of making materials with antimicrobial activity is to
disperse a chloride salt of sodium or copper or iron in water at a
concentration that remains in solution when the water is combined with an
alcohol solvent, including, but not limited to, isopropyl alcohol and
ethanol. The fibrous matrix materials for impregnation are then immersed
in a bath of the chloride ions so that the material is completely
immersed. After a suitable time the material is then removed and blotted
of excess chloride-containing solvent. Then the material is immersed in a
similar aqueous/alcohol bath that contains silver and copper or iron
ions. After a suitable time, the material is removed, blotted of excess
reagent and air dried. It is desirable that the ratio of water to alcohol
in mixtures that contain the ionic elements not exceed a concentration
that would cause hydrophilic materials to begin to gel. A preferred range
comprises 5-15% aquaeous, it is highly preferred that the aqueous portion
not be greater than 50%. Reversal of the immersion sequence is
inconsequential to the success of impregnation of the fibrous materials.

[0115]An alternative method for the impregnation of the silver compound is
to combine the silver ion and chloride ion into an aqueous component of
an alcoholic solvent bath along with copper or ferric ions before
immersion and soaking of the fibrous materials. Thereafter the fibrous
materials should be removed, blotted and air dried to form a stable
antimicrobial material for application to wounds and other compromised
tissues.

[0116]It has been found that silver salts such as silver chloride are'
generally stable in the salt form. Moreover many silver salts such as
silver chloride, silver bromide, and silver iodide as examples, are only
weakly soluble in an aqueous environment. Therefore the present invention
comprises methods of preparing a weakly soluble salt of silver on and
within the filaments of the hydrophilic material during the process and
is specifically one object of the invention. The formation of the weakly
soluble salt, such as silver chloride is done by sequentially localizing
the ions of salt within the hydrophilic material. This is accomplished by
using the aqueous-portion of the aqueous alcohol solvent bath `as the
delivery vehicle which is selectively absorbed by the material due to its
hydrophilic properties. It is possible that some delivery of ionic
species is accomplished also by the permeation of the alcohol carrying
ions into the matrix as well. The coincident location of the silver and
chloride ions in the preferred embodiment result in nucleation of a
colloidal-like structure within the matrix. The use of a bath that is
predominately composed of an organic solvent such as alcohol or any other
solvent that does not cause gelling or swelling of the fibrous materials
is desirable. This is important in that it prevents the need for
substantial dehydration of the fibrous materials following immersions as
well as for allowing recovery, and re-use of the baths for treating other
materials.

[0117]The nucleated silver salt within the matrix is immobilized and
stabilized by the presence of excess chloride containing salts as well as
copper or ferric ions, similar to the materials described above, to
render the silver treated materials resistance to discoloration by light
and radiation energy. The distribution of the nucleated silver salt is
such that when the material becomes in contact with aqueous substrates
such as wound fluid, there will be some solubilization of the silver salt
thereby releasing silver ions which are antimicrobial. The rate of
release is controlled by the inherent solubility of the silver salt, the
amount of silver and the available moisture which are taken into
consideration to provide sustained release of antimicrobial activity from
the treated materials.

[0118]A preferred embodiment of the present invention comprises
compositions of hydrophilic fibrous materials such as cross-linked
carboxymethylcellulose, calcium alginates and textiles such as cotton
that have been impregnated by the methods of the present invention to
form materials that possess antimicrobial activity which is released in a
sustained manner over time and is stable to discoloration by light
energy.

[0119]The antimicrobial matrices taught by the present invention can be
formed into a variety of devices, especially preferred are those that
polymerized polymers or plastics. Such matrices may also be coated onto
devices to provide antimicrobial activity to the surfaces of such
devices. The many uses of the compositions and devices of the present
invention are not limited to the examples given here, but include
polymeric matrices and their uses known to those skilled in the art. For
example, the present invention contemplates using the matrices for adding
antimicrobial characteristics to cosmetic products such as dressings,
topical lotions, or compresses for acne and blemishes, scar reduction,
tattoo removal, and laser resurfacing; to body contact medical
devices(such as catheter and guidewire coatings, ostomy appliances,
respiratory and feeding appliances, contact lenses, and hearing aids; and
to personal and skin care products such as skin conditioners, barrier
creams, lubricating preparations, and super absorbents for addition to
diapers, adult incontinence products, and feminine hygiene products.

[0120]Stranded Structure

[0121]The devices of the present invention may take many physical forms,
however, some preferred embodiments are constructed of thin strands of
matrix suitable for placement into the wound bed or cavity. The preferred
devices may be constructed from one or multiple strands of matrix. When
multiple strands are used in the construction, the strands are secured
together by wrap, tie, glue, or alternatively by a continuous bridge of
matrix between adjacent strands. Multiple strands are secured together to
minimize accidental loss during removal of the dressing from the wound
bed. Typically, the strands of particular embodiments are bound or
secured in the mid-region so that the ends of the device may float free.
The advantage of free floating strands is to enable the individual
strands to access a maximum volume of the wound and thereby absorb the
excess fluid, exudate and debris. The mechanical action of the free
floating strands contributes to the trapping and removal of cellular and
wound debris. Concurrently the free floating strands also conform
optimally with the contours of the wound surface to maximize contact
between the device and the wound bed.

[0122]Referring now to the drawings, one preferred conformation of the
wound dressing devices of the present invention is now described. This
preferred conformation is useful for the control of exudate moisture
accumulation, for stimulation of mechanical and autolytic debridement,
and for delivery of active agents.

[0123]FIG. 1 is a three dimensional view of a preferred embodiment of the
wound dressing device 10 with a strand 20 of the multi-strand device with
free floating strand ends 40. The strands are secured together by a
bridge 30 created during the cutting stage and composed of the matrix
material used to construct the device. FIG. 2 represents a cross-section
22 of a strand 20 of the multi-strand device 10. It is intended that the
cross-section 22 illustrate the sum of the linear dimensions of the
sides. Preferably the sum of the linear dimensions of the sides is at
least twice the numerical value of the surface area of the cross-section
to provide an adequate surface area to volume ratio of the strands. More
preferably, the sum of the linear dimensions of the sides is four or more
times the numerical value of the surface area of the cross section.

[0124]FIG. 3 is an illustration of the pattern of a die 45 used for
cutting a preferred embodiment of the wound dressing device 10 from an
appropriate matrix material. Cutting blades 55, around the perimeter of
the die, release the cut-out from the stock sheet of matrix during the
cutting phase of production. Within the perimeter, a series of cutting
blades 57 are situated lying parallel to one another extending from the
ends of the pattern toward the center but not continuing through the
center so as to leave a region 50 of uncut material in the center. The
pattern of blades may vary according to the purpose of the wound dressing
device. For example, the patterns may vary in terms of numbers of strands
20, numbers of regions of uncut region 50 for bridging strands, and the
positioning of the single or multiple bridges 50 relative to the ends of
the strands. The cross section 22 of the strands may be any suitable
dimension that allows the appropriate interaction between strands and
wound environment. The matrix may be any non-dissolving material that is
suitable for contacting the broken skin, and underlying tissues including
non-absorbent natural or synthetic materials, or absorbent natural or
synthetic materials.

[0125]FIG. 4 illustrates a pattern that is an alternative embodiment. It
is a circular pattern for making an embodiment 80 whereby the strands 90
radiate away from a central region of uncut matrix that joins the
adjacent strands in the unit. FIG. 5 illustrates a pattern for making an
embodiment whereby the bridge 95 of matrix is offset to one end of the
pattern enabling the strands 100 to radiate away from the bridge in a
single direction. FIG. 6 illustrates a pattern for making an embodiment
whereby the strands 120 are irregular in shape over their length from the
matrix bridge 100. FIG. 7 illustrates a pattern for making an embodiment
whereby the strands are conjoined at several bridges along the length of
the device and at the ends of the device. It is to be understood that the
pattern can be any variation of these embodiments and is still within the
scope of the present invention.

[0126]The unique stranded embodiment is particularly desirable because it
enables the device to maintain its integrity and also maximize the
surface area to volume ratio of its matrix. This is important since the
matrix may be an absorbent material where a high surface area to volume
ratio increases the rate of absorption, without increasing the overall
absorption capacity of the device.

[0127]In a preferred embodiment, the wound dressing is principally
constructed of a "stranded" matrix, which allows for optimal contact
between the strands and the wound area. In addition, the stranded matrix
construction maximizes the overall flexibility and pliability of the
dressing. In embodiments of the device where multiple strands are
employed, the overall flexibility and conformational characteristics of
the device are maintained by binding strands in only limited and
restricted areas. Minimal binding of the strands prevents the formation
of rigid areas and allows for the effective and optimal utilization of
numerous strands in a single device without adversely diminishing contact
with the surface of the wound bed.

[0128]Preferred embodiments of the present invention comprise stranded
matrices with antimicrobial activity. Preferably, the embodiments
comprise antimicrobial activity provided by the methods of silver
incorporation into the matrix.

[0129]Another advantage of the stranded matrix construction is the
"semi-porous" quality of the wound dressing that allows for the removal
of extraneous cellular matter resulting during the wound healing process.
The air in the inter-strands area of the device serve as a reservoir of
space that may be displaced allowing for the removal of excess materials
such as exudate fluid, debridement product and cellular exudate from the
wound bed. As this region fills, the device may swell to provide
"support" to the wound bed and surrounding tissues. A wound constitutes
damaged or "missing" tissue, and when tissue is missing, the surrounding
tissue may "collapse" or sag into the void. "Support" in this context
therefore, means the temporary filling of the void to hold the
surrounding tissue in place where it should reside.

[0130]Removal of debridement product and cellular exudate is further
facilitated by unbound, loose strands of the wound dressing devices. When
placed upon a wound, the loose strands of the devices randomly orient in
the wound bed where the thin filamentous strands and free floating ends
contribute to mechanical debridement of necrotic slough. Since the
strands are secured and bound in at least one region, a mechanical union
is formed, ensuring that all strands and necrotic tissue accumulation in
the inter-strand spaces are removed from the wound when the device is
changed. By contributing to the removal of extraneous wound products and
cellular debris, the wound dressing device permits cleaning of the wound
which in turn prevents and decreases the possibility of infection and
contamination.

[0131]In one embodiment, the wound dressing device is constructed from a
matrix composed of an absorbent synthetic polyacrylate material. The rate
of absorption of polyacrylate is significantly increased by cutting the
material into strands, which increases the surface area to volume ratio.
Polyacrylate material is particularly suitable for the wound dressings of
the present invention because it retains its integrity during interaction
with wound exudate moisture, as well as with necrotic tissue and wound
debris. The wound dressing device of the present invention does not
dissolve, gel or otherwise disintegrate during application to the wound.
The preferred matrix swells slightly during the absorption of moisture,
causing the device to conform closely to the walls of the wound bed.

[0132]In a preferred embodiment, the polyacrylate matrix is cut into
free-floating strands bound together through a matrix-bridge in the
mid-region. This pattern of construction imparts a significantly high
surface area to volume ratio for rapid moisture movement within the
absorbent matrix.

[0133]Wound dressing devices of the present invention may be produced by
cutting a desired design pattern from stock sheets of matrix material.
For example, the material may be die-cut from stock sheets of an
absorbent polyacrylate wound dressing material. The stranded cut-out may
then be coated with an agent to prevent aggregation and tangling of the
free floating strands. Coating agents that may be used include, but are
not limited to, petrolatum, talcum, polyglycols, glycerol, propylene,
glycol, vegetable oil, and animal oil. Following the steps of cutting and
coating, the material may be sterilized using sterilization techniques
known in the art such as gamma radiation, steam and heat sterilization,
electron beam or chemical sterilization (such as by use of ethylene
oxide).

[0134]A preferred composition of the present invention comprises a matrix
comprising a scaffolding polymer, a non-gellable polysaccharide, and one
or more active agents incorporated therein. A more preferred matrix
comprises an acrylamide polymer, guar gum, and one or more active agents
incorporated therein. A most preferred matrix comprises an acrylamide
polymer, guar gum, has one or more active agents incorporated therein,
and is formed into a stranded structure wherein the strands are secured
by at least one common region.

[0136]In particular, the wound dressing devices of the preferred
embodiments are especially applicable for usage on heavily exudating
acute and chronic wounds for controlling accumulating exudate moisture,
support of the wound bed and surrounding tissues. Importantly, the wound
dressings are particularly effective for stimulating and supporting
autolytic debridement, and therefore accelerating the wound healing
process.

[0137]In use, the wound dressing devices of the present invention are the
primary dressing placed in direct contact with the wound bed, or as near
as practical against the wound bed. The devices may serve as a packing
material and, if required, may be secured into position with any suitable
secondary wound dressing such as a wrap, tape, gauze, or pad. The
dressings are temporary, however, and are not intended for permanent
incorporation into the healed tissues. When necessary, the wound dressing
devices are changed by first removing any over-dressing material and then
removing the device, whereby any accumulated necrotic tissue and exudate
is lifted away. The wound dressing devices of the present invention may
be replaced by a fresh device or other suitable wound covering.

[0138]The devices may be placed in their entirety into a wound, placed in
combination with additional bundles of the same design into the wound, or
cut through the bridge between strands to reduce the size or number of
strands present in the wound.

[0139]The devices of the present invention may be cut, shaped and modified
to accommodate numerous uses and applications. For example, the devices
may be used as a gastric retrievable device, wherein a retrieval cord is
attached to the device that is then swallowed. After absorption has taken
place, the devices may be retrieved and analyzed for content.

[0140]The devices may undergo a swelling action as they absorbs exudate
moisture, however, they will not dissolve or disintegrate. The swelling
action displaces necrotic material from the wound surface and forces the
material into the inter-strands regions of the device. The laden moisture
content and the retention of moisture near the wound bed by the invention
contributes to stimulation of the autolytic debridement process whereby
the body's own enzymes break-up necrotic tissue and cellular debris.
Complete removal of the device occurs due to the conjoined nature of the
device.

[0141]The foregoing description includes the best presently contemplated
mode of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the inventions and
should not be taken in a limiting sense. This invention is further
illustrated by the following examples, which are not to be construed in
any way as imposing limitations upon the scope thereof. On the contrary,
it is to be clearly understood that resort may be had to various other
embodiments, modifications, and equivalents thereof, which, after reading
the description herein, may suggest themselves to those skilled in the
art without departing from the spirit of the present invention.

EXAMPLE 1

Formation of a Matrix Including Acrylamide

[0142]A mixing tank was charged with 161.4 kg of water and 9.1894 kg of
acrylamide, 0.10347 kg of NNNN'-methylenebisacrylamide, and 9.3046 kg of
glycerol were added and mixed. Then 1.0213 kg of guar gum non-gellable
polysaccharide was dispersed in a mixture containing 0.9770 kg of
isopropyl alcohol and 2 kg of water. The solution of guar gum was then
added and dispersed into the acrylamide mixture. After suitable mixing,
0.1042 kg of TEMED was added and polymerization was catalyzed with 0.0999
kg ammonium persulphate.

[0143]While the batch was still liquid, it was poured into molds to form
sheets. After gelling had occurred, sheets were transferred to a
dessicator and dehydrated to form a stable intermediate stock sheet.
Prior to cutting to size, the stock material was re-hydrated in a humid
atmosphere. After cutting, the material was coated with petrolatum. The
resulting wound dressing device was then sealed into appropriate
packaging and irradiated to sterilize it.

EXAMPLE 2

Absorption Capacity of Polyacrylamide Matrix

[0144]It was determined that a preferred matrix material composed of
cross-linked polyacrylamide and embedded natural vegetable gum absorbed
approximately seven times its weight in water. Saturation of a flat sheet
of matrix material with a thickness of 0.9 mm was achieved in
approximately 22 hours of continuous exposure to excess water. A
similarly sized piece of flat matrix material was cut into thin strands
with a calculated 200% increase in overall surface area. The total water
absorption of this material was also approximately seven times its
weight. However this material achieved saturation in approximately five
hours. Similar comparisons were made between an intact matrix and a
matrix cut in such a way as to increase the surface area between 150% and
300%. These studies revealed that the matrices retained their overall
absorption capacity but there was an increased rate of absorption
proportional to the increase rate of absorption proportional to the
increase in surface area.

EXAMPLE 3

Matrix Absorption Capacities for Various Natural Substances

[0145]Matrices, cut into strands, were tested for absorption capacities on
a variety of natural aqueous based viscous fluids. These fluids included
water containing salt (0.15 M salinity), cow's whole milk, egg whites
from yogurt, and fetal bovine serum. The absorption of moisture by the
test matrix strands ranged between 3.2 and 7.3 times the original weight
of the tested devices.

EXAMPLE 4

Absorption Capacity of Matrix in Heterogeneous Biological Fluid

[0146]A polyacrylamide matrix of a preferred device was placed into a test
tube containing fetal bovine serum, in an amount equal to five times the
weight of the matrix. The matrix absorbed the aqueous fluid from the
serum, leaving a concentrate of serum proteins in approximately four
hours at 4° C. The concentrated serum proteins were predominately
located between the strands of the device as a thick viscous coagulation.
When the device was removed from the tube, the concentrated proteins were
also removed. This experiment showed that the design would assist in the
debridement of the wound.

EXAMPLE 5

Construction of Stranded Matrices

[0147]Initial prototypes of the stranded matrices were prepared by taking
flat sheets of polyacrylamide matrix and cutting them into thin strands
using a sharp instrument such as a box knife. Several methods were tested
to determine a satisfactory method for commercial production of the
device. The following tests were carried out with success:

[0148]Test 5(a). Matrix material was processed through a pasta cutter
using a blade for noodles.

[0149]Test 5(b). A steel rule die was constructed such that parallel bands
of steel rules, separated by spacers were locked into a die block. Matrix
was cut by placing the die over the matrix and press-cutting with a
hydraulic press.

[0150]Test 5(c). Matrix formula was compounded and catalyzed to initiate
polymerization. The matrix was then placed into a 50 ml syringe and
extruded as a thin strand onto a sheet. The thin strands were allowed to
complete polymerization and then were dried and cut to uniform lengths
for use in the device.

[0151]Test 5(d). A rotary die was constructed with a preferred pattern.
The rotary die was placed into the rotary die assembly and matrix was fed
through between the rotary die and the anvil for cutting.

EXAMPLE 6

Optimization of Matrix Construction Utility

[0152]Several prototypes were constructed to optimize the utility of the
device as follows:

[0153]Test 6(a) Individual strands cut from a sheet of matrix were banded
together using a silicone elastomer ring. The ring, having an internal
diameter of approximately 3 mm and a length of 1.5 mm, was stretched open
so that between five to seven strands could be threaded through and
secured by the band about the middle. When placed into fluid for
absorption studies, it was found that the unit nature of the device was
retained throughout the absorption period and that the whole device was
removed without leaving remnants in the absorption chamber.

[0154]Test 6(b) Prototypes constructed by using one strand to tie other
strands together performed satisfactorily in absorption and retrieval
studies.

[0155]Test 6(c) Prototypes constructed by maintaining a continuous bridge
of matrix between adjacent strands were tested and shown to perform
satisfactorily in absorption and retrieval studies.

EXAMPLE 7

Incorporation of Penicillin G into the Matrix

[0156]The incorporation of the antimicrobial agent, penicillin G, into the
matrix was evaluated by dissolving 1×106 units of penicillin G
powder into 50 milliliters of water. Acrylamide, methylenebisacrylamide,
glycerol, and a guar gum/isopropyl alcohol mixture were added to a flask
containing 900 ml water and mixed for two hours. The penicillin solution
was then added to the flask along with TEMED dissolved in 25 ml water.
After thorough mixing, ammonium persulphate in 25 ml water was added and
mixed thoroughly. The mixture was then poured into sheet molds and
allowed to gel. The sheets of semi-solid gel material were stripped from
the mold and dehydrated to approximately 7% their original water content
for storage. Prior to testing, the sheets were placed in a humidified
environment until the sheet weight had increased to approximately
118-122% the storage weight. Discs of 0.7 cm diameter were cut from the
sheets. The discs were placed onto the surfaces of agar plates that had
previously been seeded with various strains of microorganisms (Staph
aureus; E. coli, Candida albicans; Ps aeruginosa). The plates were
incubated and then examined for zones of inhibition around the discs
containing antibiotic verses control discs. Zones of inhibition were
measured around the penicillin containing matrix but not the control
matrix on the Staph aureas, E coli, and Pseudomonas aeruginosa plates. No
zone was measured on the Candida albicans plate. These results
demonstrate the release of active penicillin G after its incorporation
into the matrix.

EXAMPLE 8

Incorporation of Silver Chloride Precipitate into the Matrix

[0157]Silver chloride is a weakly soluble salt that dissociates in water
to release the silver ion that may have antimicrobial activity. Silver
nitrate was dissolved into the batch mixture of pre-polymerized matrix at
a concentration of 5×10-3 M and then mixed well. The silver
was precipitated by the addition of sodium chloride to produce a
colloidal suspension of the weakly soluble salt. The batch was then
polymerized by the addition of TEMED and ammonium persulphate and cast
into sheets. The sheets were dehydrated to approximately 5% of the
original moisture content and stored in the dark. Before testing, the
sheet stock was hydrated to 118-122% its storage weight and then cut into
0.7 cm discs that were placed on the surface of pre-inoculated agar
culture plates. The plates were incubated and then evaluated for growth
around the discs.

[0158]Zones of inhibition were measured around discs on plates inoculated
with Staph aureus; E. coli; Candida albicans; Pseudomonas aeruginosa,
indicating the release of active silver ions after incorporation into the
matrix. Hydrated sheets exposed to continuous light turned from an amber
color to a uniform tan to brown color which illustrated uniform
dispersion of the silver chloride precipitate. This also showed the
susceptibility of the product to discoloration due to exposure to light
when a stabilizing solution such as that of copper or ferric ions, was
not added to the mixture.

EXAMPLE 9

Synergistic Action Between Therapeutic Agent and Adjuvant

[0159]The antifungal agent Zn-pyrithione is an active agent against a wide
range of pathogenic fungi but it poorly penetrates heavily keratinized
tissues such as finger and toe nails. Matrix material containing
Zn-pyrithione and the keratinolytic agents salicylic acid and urea were
tested for increased efficacy of delivering agents to control fungal
growth in nail tissue. To the pre polymerized batch material was added
sufficient Zn-pyrithione, salicylic acid and urea to give final
concentrations of 0.01%, 5% and 5%, respectively. The batch was
neutralized to pH 6.5 by the addition of sodium hydroxide. After thorough
mixing, the batch was poured into molds to cast into sheets. After
gelling, the sheets were dehydrated to 5% the original moisture content
and stored. Before testing, the sheet stock was hydrated to 118-122% its
storage weight and then cut into 0.7 cm discs which were placed on the
surface of bovine hoof material cut thinly to resemble finger nail. These
were then transferred onto pre-inoculated agar culture plates. The plates
were incubated and evaluated for growth around the discs.

[0160]Zones of inhibition were measured around the discs on plates
inoculated with Candida albicans. No zones were measured where
Zn-pyrithione or the keratinolytic agents were not included in the
matrix. Smaller zones were measured where only urea and Zn-pyrithione
were added. Zones of inhibition were however measured around sets that
contained both the active agent and the keratinolytic agents in
combination. These results demonstrate that therapeutic agents and
adjuvants may be incorporated into the matrix and later released in
active form such that they work synergistically.

EXAMPLE 10

Bovine Protein Incorporation into and Delivery from the Matrix

[0161]Bovine serum albumin (approximately 65,000 Daltons) and bovine gamma
globulin (approximately 155,000 Daltons) were dissolved at a
concentration of 0. 1% w/w into a pre-polymerized matrix batch material
and thoroughly mixed. The batch was polymerized by the addition of TEMED
and ammonium persulphate, poured into molds and gelled into sheets. The
sheets were dehydrated to approximately 5% the original moisture content
and stored. Before testing, the sheet stock was hydrated to 118-122% its
storage weight and then cut into 0.7 cm discs which were placed on the
surface of saline agar plates. The plates were incubated for 24 hours at
4° C. and then developed by the addition of 0.25 M HCl solution
which causes proteins to precipitate. Zones of protein precipitate were
measured only around the discs that had protein incorporated into the
matrix, indicating the release of active protein after its incorporation
into the matrix.

EXAMPLE 11

Interleukin-2 Incorporation into and Delivery from the Matrix

[0162]The growth factor interleukin-2 was incorporated into polymerized
matrix material by soaking re-hydrated plain stock sheet in fluid
containing the growth factor. After 24 hours of soaking at 4° C.,
the matrix pieces were cut into one cm circles and placed into saline.
Samples of the elution fluid were taken at intervals and assayed by ELISA
(Enzyme Linked Immunosorbent Assay) for interleukin-2 to determine if
material entered the matrix and was then released. The results showed
that proportionately more IL-2 was eluted from the matrix over time.

EXAMPLE 12

Temporal Release of Antifungal Agent

[0163]Fluconazole was incorporated by the addition of the active agent to
a pre-polymerized batch of matrix. After polymerization, dehydration and
rehydration, a disc containing the active agent was placed onto an agar
plate for two hours at 4° C. Thereafter; every two hours for a
total of 154 hours, the disc was removed and transferred to a new spot on
the surface of the agar. After all transfers had been carried out, the
plates were inoculated with Candida albicans and incubated at 35°
C. until confluent growth had occurred. The serial transfer spots on the
plates were then examined for zones of inhibition. The results showed
that the device delivered a high dose of fluconazole in the first eight
hours and then a steady concentration thereafter until the 140th hour
when the concentration, according to zone size, began to diminish.

EXAMPLE 13

Delivery of a Biologically Functional Protein from the Matrix

[0164]Human transferrin is an iron chelating protein of approximately
70,000 MW. Transferrin was incorporated into the pre-polymerized batch
mix at 0.05% w/w, mixed, and then encapsulated by polymerization with
TEMED and animonium persulphate. After dehydration, rehydration and
cutting, discs of 0.7 cm were placed onto the surface of nutrient agar
plates and incubated at 4° C. for 24 hours. The discs were then
removed and the plates were inoculated with Staph aureus and then
incubated at 37° C. overnight. The plates were examined for zones
of inhibition where the transferrin removed the trace element iron from
the nutrient. Human transferrin retained its biological activity during
incorporation, processing and testing as measured by the zones of
inhibition around the spots where transferrin-containing discs had been
placed.

EXAMPLE 14

[0165]A wound healing device comprising a polyacrylate hydratable matrix
produced according to U.S. Pat. No. 5,196,190 and containing silver was
made using the following steps. The silver containing polyacrylate matrix
was made by mixing 185 g acrylamide and 2 g bisacrylainide into 3330 g of
water containing between 33.3 g of sodium chloride. To this mixture, was
added 21 g of guar gum and 188 g of glycerol. After mixing to
homogeneity, a solution containing 0.563 g silver nitrate was slowly
added to the mixing batch. After formation of the finely dispersed silver
complex, either from 0.16 g copper chloride (CuCl2) or 0.46 g ferric
chloride FeCl3 was dissolved into the mixture.

[0166]The polymerization of the mixture was accomplished by blending 1.8
ml TEMED and 2.6 g ammonium persulphate into the mixture. The mixture was
poured into the appropriate molds before polymerization in a dark place.
The gelled polymer was removed from the mold, dehydrated by mild heat in
a darkened drier and then rehydrated by humidification to a desired
moisture content, 22% w/w. The matrix was then cut if necessary,
packaged, and sterilized by irradiation of electron beam or gamma
irradiation.

EXAMPLE 15

[0167]This Example shows the antimicrobial activity of the
silver-containing matrix wound dressings of Example 14 in a zone
inhibition assay. Fresh overnight suspension cultures of each of various
medically important bacteria and fungi were coated onto the surface of
trypticase soy agar, for bacteria, or Sabouraud's agar plates, for fungi.
Circles 5 mm in diameter, were cut from the silver-containing dressings
and from control dressings that do not contain silver. The circles were
placed on the surface of the cultured plates which were then incubated
for 24-48 hours. Zones of inhibition were measured at the completion of
the incubation phase. The diameter of the zones were measured and are
expressed in Table 1.

[0168]This example was directed to showing that the devices of the present
invention, comprising a matrix with silver incorporated, such as those
made by the methods of Example 14, was stable to light. This was done by
preparing 1 inch circles of silver-containing matrix that were then
stored in the dark. Each day for 7 days a 1 inch circle of matrix was
transferred from dark to a lighted area so that at the end of the
7th day a total of 8 circles had been exposed to light for between 0
time and 7 days.

[0169]Dressing circles that contained silver chloride without the
photostablization chemistry were treated identically. The dressings that
had no photostabilization chemistry had reacted by the formation of a
blackening in the matrix. The blackening was proportional to the amount
of time the matrix had been exposed to light. By contrast samples that
were stabilized by either copper or iron did not show discoloriazation.

EXAMPLE 17

[0170]The sustained release of silver was shown in this example using the
dressing made in Example 14. This was demonstrated by seeding agar
nutrient plates with a test strain of microorganisms daily for 6 days.
The trypticase soy agar were inoculated with a fresh overnight inoculum
of Staph. aureus. The plates were then incubated for 24 h at 37°
C. The zones of inhibition were then measured before transferring the
dressing circles to a freshly inoculated plate of TSA. This process was
repeated daily for 5 days to measure the release of antimicrobial
activity into the culture plate.

[0171]To clarify, on day 1, a piece (5 mm circle) of silver-containing
dressing was placed on the first plate and incubated for 24 hours. The
circle was then transferred to the second plate for a further 24 hours
and so on. Each plate was then incubated to determine the zone of
inhibition around the area where the piece of matrix had been deposited.
FIG. 8 shows the data of the silver-containing dressing and a control
dressing that did not contain silver. The result's showed that silver was
released over a period of 6 days in a concentration sufficient to inhibit
the growth of the indicator strain of bacteria used in the test.

[0172]Tissue cytotoxicity was evaluated by the in vitro method taught in
the AAMI Guidelines for Biological Evaluation of Medical Devices. Samples
of the silver-containing wound dressings of Example 14 were added to DMEM
tissue culture medium and incubated. Fetal bovine serum was added before
the samples were transferred to confluent monolayers of L-929
fibroblasts. The cultures were incubated at 37° C. in 5% CO2
for 24 h. Alamar Blue vital dye was added for the last 4 h of incubation.
The culture supernatants were removed, assayed for OD difference at 570
and 600 nm wavelength along with the positive (fresh medium alone) and
negative (3% w/v acetic acid in saline) controls. The viability of
fibroblasts was also evaluated by parallel cultures stained with the
vital dye, trypan Blue (data not shown). The silver-containing dressing
was indistinguishable from the positive growth control sample with
greater than 99% of fibroblasts over the culture period. The acetic acid
solution caused a greater than 88% decrease in viability in the
fibroblasts culture. These findings are consistent with microscopic
observation of cultures treated with trypan blue vital dye (data not
shown). FIG. 9 shows the results of the silver-containing dressing and
the positive and negative controls.

EXAMPLE 19

[0173]This Example shows the absorbency profile of the silver-containing
dressings of the present invention, such as that made by Example 14.
Squares (2.5 cm) were cut from the matrix of Example 14 that does not
contain silver, and the silver-containing dressing. These were weighed
and then placed into isotonic saline solution at room temperature. At
various intervals, each matrix was removed, damped of excess moisture and
reweighed. This procedure was repeated over the course of 24 h. The
hydrophilic base polymer alone increased by 720% in saline. The addition
of silver to the matrix only slightly reduced its absorbency (605% vs
720%). FIG. 10 shows the absorption profile and the donation of moisture
by the silver-containing dressing.

[0174]Donation of moisture testing was carried out by weighing the silver
polyacrylate material onto dried pre-weighed filter paper and allowing it
to stand for various intervals before re-weighing to detect moisture
donation.

EXAMPLE 20

[0175]This Example was directed to showing the light stability and skin
staining characteristics of silver-containing wound care dressings. Ionic
silver (Ag+) is reduced to a black precipitate (Ag°) by light
energy. The silver-containing matrix of Example 14 suppressed the light
reaction of silver. This was demonstrated by exposing 2.5 cm circular
samples of silver-containing matrix to light for various numbers of days.
There was almost no darkening of the silver-containing dressing for up to
8 days of exposure to room light. By contrast, silver nitrate impregnated
filter papers showed significant darkening within 24 h exposure to light.

[0176]When placed on skin and exposed to light, similar results were seen.
The silver impregnated paper stained the skin whereas the
silver-containing matrix did not.

EXAMPLE 21

Rate of Bacterial Killing

[0177]The time between exposure to the antimicrobial and the bactericidal
event is related to the rate of release of silver from the matrix. The
rate of killing of E. coli by silver-containing matrix from Example 14
was determined by suspending a 1 gram sample of matrix in a bacterial
suspension. After various time intervals samples were removed and plated
counted to determine the number of surviving bacteria. FIG. 11 is a plot
of the number of surviving organisms at the various sample intervals
following exposure to the silver-containing matrix.

EXAMPLE 22

Skin Bioburden

[0178]Continued silver ion formation and release from the silver
containing polyacrylate is dependent upon disruption of the equilibrium
between colloid and free ions in the aqueous phase of the matrix.
Theoretically even small amounts of aqueous fluid added to the matrix
will cause additional release of silver. Furthermore this released silver
should be sufficient to be bactericidal to organisms in contact with the
dressing.

[0179]This was illustrated by placing either silver-containing matrix of
Example 14 or non-silver containing matrix on skin for a set time
interval and then sampling under each of the matrices for surviving
bacteria. Samples of matrix from example 14 along with plain non-silver
containing matrix was placed on adjacent areas of the forearms of
volunteers. 24 h later the specimens were removed and the areas in a
precise 30 mm circle were swabbed and plated and counted to determine the
microbial bioburden. The plain matrix served as the control for each of
the five individuals. In all cases the presence of silver significantly
decreased the bioburden compared to the plain matrix (see FIG. 12). Each
line is the test of one individual.

EXAMPLE 23

Biocompatability Testing

[0180]Devices containing bioactive ingredients must be compatible with
tissues to have utility in clinical applications. This is generally
determined by testing the devices for their propensity to cause
irritation or to induce sensitization. Skin irritation testing was
carried out by securing 30 mm diameter pieces of the matrix of Example 14
to the forearms of volunteers for 7 days. Plain matrix without silver
(FlexiGel) served as the known non-irritating control. Latex served as a
probable irritating material. Specimens were secured by a polyurethane
thin film adhesive dressing. At the conclusion of the induction phase the
materials were removed and the areas were scored for erythema and
induration consistent with irritation (see results in the table 2).

[0181]Sensitization is the induction of an immunological response to
agents or sensitizers in the material. This was measured by the local
lymph node assay which is carried out by placing test materials on the
ears of mice each day for 5 consecutive days. On the fifth day the
animals received a dose of radioactive thymidine for a pulse period of 4
hours. Thereafter the local draining lymph nodes were removed from the
animals and measured for thymidine incorporation. The higher the level of
incorporation the more sensitized the animals. The findings laid out in
table 2 showed that none of the animals were sensitized to the
silver-containing matrix of Example 14.

[0182]Example 24 was directed to the development of methods for the
nucleation of silver chloride in Aquacel (carboxymethoylcellulose, CMC)
using water in IPA (Isopropyl alcohol) or EtOH (ethanol) as the delivery
and permeation vehicles. One aspect of this Example was to establish
solvent to water ratios for the precipitation of silver chloride into
preformed filamentous materials such as Aquacel (CMC) and alginates.

[0183]Aquacel and alginates are hydrophilic materials that aggressively
absorb aqueous solutions which often cause gelling of the matrix
materials. Gelled materials may be subsequently dehydrated, but seldom
retain their original properties after absorption of water. Therefore it
is impractical to use a substantially aqueous vehicle for the delivery of
ionic silver and chloride into the matrix material where nucleation in
situ of colloid would be expected to occur. This excludes the method of
precipitating AgCl in situ using water as solvent. Aquacel and alginates
do not absorb alcohol, therefore a AgCl precipitation in a water; alcohol
solution to partially hydrate fibers with reagents can be done.

[0184]A. This experiment of the Example showed the use of either acetone,
isopropyl alcohol or ethanol as the solvent phase of an aqueous:alcohol
bath for impregnation of silver into cross-linked carboxymethylcellulose.

[0185]The following combinations of reagents were produced and tested for
efficacy in allowing nucleation of AgCl in the solvent phase.

[0190]It was concluded that the ethanol was the preferred alcohol for the
delivery vehicle.

[0191]B. This experiment was carried out to determine if separate
aqueous:alcohol solutions could be pre-made and then combined before the
immersion of hydrophilic materials as an appropriate single bath method
for impregnating hydrophilic polymers. Separate reagents were prepared
according to the formula below and then combined together.

[0192]1) Add 0.221 g AgNO3 to 200 uL H2O to 25 g EtOH

[0193]2) Add 0.5 g NaCl to 2 mL water to 25 g EtOH

[0194]Combine Solutions

[0195]Results: Immediately following combining of the reagents a heavy
rapidly forming precipitate developed in the mixture. It was not
appropriate to pre-mix separate solutions that are later combine to form
the bath for the immersion of hydrophilic matrix material for
impregnating with silver.

[0196]C.

[0197]The purpose of this experiment was to determine if sodium
thiosulfate dissolution of silver chloride would aid in the deposition of
the antimicrobial silver in hydrophilic fibers. The reagents were
prepared in the following fashion and observed for the formation of a
fine precipitate after combination with either alcohol or water.

[0198]1. Add 0.177 g NaCl to 4 ml H2O

[0199]2. Add 6 ml AgNO3 sol (0.11325 g/50 ml H2O

[0200]3. Add 0.015 g Na thiosulfate to dissolve AgCl

[0201]4. Add to 90 ml H2O, half to 90 ml EtOH

[0202]The test showed that the addition of the reagent with sodium
thiosulfate with ethanol allowed the formation of a precipitate but none
formed when the reagent was added to water.

[0203]Sodium thiosulfate may interfere with nucleation of silver chloride
in hydrophilic fibers.

[0204]D. The nucleation of silver chloride colloid in the hydrophilic
polymer was accomplished by preparing an aqueous:alcohol solution of
sodium chloride in which various hydrophilic materials were immersed.
After an appropriate time an aqueous:alcohol solution containing silver
nitrate was added. The materials were then removed, blotted of excess
materials and air dried. They were then tested for antimicrobial activity
against Staph aureus by zone inhibition assay, for skin staining
properties and for discoloration in light.

[0205]1) Add 0.1777 g NaCl to 2 ml H2O

[0206]2) Add 0.006795 g AgNO3 to 100 μl H2O

[0207]3) Add 25 g EtOH to NaCl and AgNO3 solutions

[0208]4) Place a 2×2 in. square of Tegagen, Algisite M, Aquacel, or
Algisite Rope into the NaCl solutions.

[0217]Silver was incorporated into hydrophilic fibers in amounts that
allowed for sustained release. IPA or acetone may be used with more
soluble chloride salts (CuCl2 FeCl3) but ethanol is the
preferred solvent when using sodium chloride. The resulting materials
possess antimicrobial activity and do not appreciably discolor in the
presence of light.

EXAMPLE 25

Titration of the NaCl, Ag, Cu Concentrations for Effecting Impregnation of
Stabilized Silver Into Aquacel

[0218]This Example was designed to develop a method for incorporating AgCl
into Aquacel fibers to form a color stable, sustained release
antimicrobial hydrophilic material for wound care applications.

[0219]It is possible to add AgCl to fibers so that it may be released over
a sustained period of time. Sustained release characteristics are
imparted by the size and location of nucleated silver chloride in the
hydrophilic fibers. The stability of the material to light is controlled
by the amount of NaCl, and the location and concentration of Cu ions in
the material.

[0220]The following ratios of reagents were prepared and used to
impregnate 2×2 inch samples of carboxymethylcellulose (Aquacel).
The stock solution of silver used in these tests was 0.11325 g Ag/50 mL
H2O. The stock solution of copper ions was 0.0495 g Cu/10 g EtOH.

[0236]Samples were immersed then removed from the bathes and blotted then
dried in air. A portion of each sample was exposed to light as well as
for antimicrobial activity against Staph aureus.

[0237]Results:

[0238]Samples that contained higher concentrations of silver discolored
more quickly in light with most samples eventually turning a purplish
color. The exceptions were samples "n" and "o" which remained white. With
the exception of the sample developed from the combination in "o", the
samples had an acceptable feel and texture. Sample "o" was stiff
following processing. All samples produced the same size zone of
inhibition on the staph plate except for sample "o", which had no zone of
inhibition.

EXAMPLE 26

A Comparison of Silver Chloride Nucleation in Solutions Containing Both
Silver and Chloride Ions vs. Separation of the Reagents

[0239]Previous evaluations of the process incorporated the silver into a
bath that contained the hydrophilic fibrous materials. This resulted in
the formation of a desirable effect but had the disadvantage that
solutions could not be re-used. This evaluation was undertaken to
determine if nucleation occurred when materials were first treated with
chloride ion containing reagent then rinsed before immersion into a
silver ion containing reagent bath.

[0240]Experimental Design: Specimens of carboxymethylcellulose were
impregnated with silver by the following methods.

[0242]Prepare an aqueous:ethanol solution by adding 0.0888 g NaCl in 2 ml
H2O to 25 g EtOH. Place a 2×2 in sample of Aquacel into the
solution for 20 seconds and then remove. Rinse in ethanol 3 times to
remove excess chloride ions from the surface then place the sample in an
aqueous:alcohol solution made by combining 0.006795 g AgNO3 in 100
μl H2O to 2 g EtOH. Allow the specimen to stand for 10 seconds
then remove, rinse and blot dry before testing for stability to light and
for sustained release of antimicrobial activity. Prepare an
aqueous:ethanol solution by adding 0.0888 g NaCl in 2 ml H2O and 500
μl Cu solution (0.0495 g Cu/10 g EtOH) to 25 g EtOH. Place a 2×2
in sample of Aquacel into the solution for 20 seconds and then remove.
Rinse in ethanol 3 times to remove excess chloride ions from the surface
then place the sample in an aqueous:alcohol solution made by combining
0006795 g AgNO3 in 100 μl H2O to 25 g EtOH. Allow the
specimen to stand for 10 seconds then remove, rinse and blot dry before
testing for stability to light and for sustained release of antimicrobial
activity.

[0243]Control samples were prepared by soaking specimens in
aqueous:ethanol solutions made by adding 0.0888 g NaCl in 2 ml H2O
with either 500 μl or 1000 μl Cu solution (0.0495 g Cu/10 g EtOH)
to 25 g EtOH. After 10 seconds of soak the aqueous:alcohol solution was
made by combining 0.006795 g AgNO3 in 100 μl H2O to 25 g
EtOH was added directly to the first mixture, allowed to stand for 20
seconds before removal, blotting and drying.

[0244]2) Blot to dry, expose to light and test for zones of inhibition
with staph.

[0245]The results showed that chasing in silver ions after chloride ion
impregnation does lead to the development of antimicrobial activity.
However the activity level was lower than that for materials developed by
adding the silver ion to the chloride ion in the same batch

EXAMPLE 27

Impregnation of Various Hydrophilic and Non-Hydrophilic Materials with the
Silver Impregnation Technology

[0246]This Example was to determine whether the solvent precipitation
method can be used on other fibrous materials.

[0247]Samples of a variety of materials were treated by the common bath
impregnation methods to convert them into sustained release antimicrobial
materials. The materials were prepared into 2×2 inch pads and
included Kaltostat alginate pad, Curity gauze sponge, NuGauze, Telfa
non-adherent pads, Kaltostat alginate rope, and Aquacel. The procedure
for impregnation was carried out as described below. Where Cu was
incorporated into the procedure it was drawn from a stock solution at
0.0495 g Cu/10 g EtOH.

[0248]Procedure:

[0249]Samples were prepared by soaking specimens in aqueous:ethanol
solutions made by adding 0.0888 g NaCl in 2 ml H2O with 500 μl Cu
solution to 25 g EtOH. After 10 seconds of soak the aqueous:alcohol
solution made by combining 0.006795 g AgNO3 in 100 μl H2O to 25 g
EtOH was added directly to the first mixture, allowed to stand for 20
seconds before removal, blotting and drying.

[0250]B. Samples were prepared by soaking specimens in aqueous solutions
made by adding 0.0888 g NaCl in 2 ml H2O with 500 μl Cu solution to 25
g H2O. After 10 seconds of soaking, the aqueous solution made by
combining 0.006795 g AgNO3 in 100 μl H2O to 25 g H2O was added
directly to the first mixture, allowed to stand for 20 seconds before
removal, blotting and drying.

[0251]Results:

[0252]Light stability testing:

[0253]Samples prepared by using fully aqueous soaks turned color quickly
even when still wet when exposed to light. By contrast the samples
prepared using the aqueous:alcohol soak were more stable to light. Telfa
treated by the aqueous:alcohol bath method did not turn color at all. The
texture of dressings treated with aqueous:alcohol were superior to those
produced in the aqueous bath which were stiff and rigid.

[0256]This Example was done to examine the effects of electron beam
irradiation on silver treated Aquacel

[0257]Experimental Design:

[0258]Samples of Aquacel were impregnated with silver along with various
amounts of copper ions by the following methods:

[0259]Samples were prepared by soaking specimens in aqueous:ethanol
solutions made by adding 0.0888 g NaCl in 2 ml H2O with 500 μl Cu
solution (0.0495 g Cu/10 g EtOH) to 25 g EtOH. After 10 seconds of soak
the aqueous:alcohol solution made by combining 0.006795 g AgNO3 in
100 μl H2O to 25 g EtOH was added directly to the first mixture,
allowed to stand for 20 seconds before removal, blotting and drying.

[0260]Samples were prepared by soaking specimens in aqueous:ethanol
solutions made by adding 0.0888 g NaCl in 2 ml H2O with 500 μl Cu
solution (0.0495 g Cu/10 g EtOH) to 25 g EtOH. After 10 seconds of soak
the aqueous:alcohol solution made by combining 0.01359 g AgNO3 in
100 μl H2O to 25 g EtOH was added directly to the first mixture,
allowed to stand for 20 seconds before removal, blotting and drying.

[0261]Samples were prepared by soaking specimens in aqueous:ethanol
solutions made by adding 0.0888 g NaCl in 2 ml H2O to 25 g EtOH. After 10
seconds of soak the aqueous:alcohol solution made by combining 0.006795 g
AgNO3 in 100 ul H2O to 25 g EtOH was added directly to the first
mixture, allowed to stand for 20 blotting and drying.

[0262]All samples were then placed in medical grade aluminum foil pouches,
heat sealed and dispatched to e-beam for irradiation. After their return
they were tested for stability in light and for sustained release of
antimicrobial activity.

[0265]The samples were equally stable against the effects of e-beam
radiation regardless of the amount of copper present. Similarly
increasing the dosage of silver did not increase the risk of
discoloration by e-beam energy.

[0268]It should be understood that the foregoing relates only to preferred
embodiments of the present invention and that numerous modifications or
alterations may be made therein without departing from the spirit and the
scope of the invention as set forth in the appended claims.